Existing location systems typically employ radio, ultrasound or optical signals to determine a position of a target object using angle of arrival (AOA), time difference of arrival (TDOA) or frequency difference of arrival (FDOA) techniques. These systems generally require supporting infrastructure such as transmitters and receivers which are external to the target and able to sense the target and/or be visible to the target. An enclosed target, for example an object in a vehicle, may not be located using these techniques.
Inertial navigation systems provide an alternative method for self location of an object in an enclosed environment. These systems use accelerometers but they require calibration and tend to drift over time thus requiring periodic re-calibration which limits their accuracy and suitability for many applications.
What is needed, therefore, are improved methods and apparatus for autonomous location of an object in an enclosed environment, and in particular, those that will not require external supporting infrastructure.